Evaluation of texture weakening and microstructural evolution in an Fe-10Ni7Mn martensitic steel severely deformed by six turns of high-pressure torsion

Abstract

The effect of high-pressure torsion (HPT) on the textural components and microstructural evolution of an Fe-10Ni-7Mn steel was investigated. Six turns of HPT, with a rotation rate of 1rpm and with a pressure of 6.0 GPa, was applied to a solution annealed steel. Microstructural and textural evolution, including dislocation characteristics and grain size/misorientation measurements, were accomplished using Electron Backscatter Diffraction (EBSD). The results
showed that a fully martensitic structure, containing a high density of dislocations, was developed during the solution annealing and subsequently the application of six turns of HPT processing converted the low-angle grain boundaries (LAGBs) of the solution annealed condition into highangle grain boundaries (HAGBs). Thus, the sub-grain boundaries established in the solution
annealed condition were altered into very sharp HAGBs. The grain size decreased from ~25 µm in the solution annealed condition to ~210 nm in the severely deformed condition after six turns of HPT and the yield strength, tensile strength and ductility were increasd from 765 MPa, 840 MPa and 15.2 % to 1890 MPa, 2230 MPa and 6.1 % in the HPT-processed sample. Applying six turns
of HPT developed a predominantly {111}//ND texture but the overal texture intensity of the HPTprocessed sample was weakened to a value of about one-quarter of the as-quenched solution treated sample. This was related to dynamic recrystallization and grain subdivision as well as a dislocation
density reduction in the HPT-processed sample. The texture components of strong Copper ({112}<111>), S ({123}<634>) and some avarage intesnsity Cube {100}<0001> were observed in the {100} pole figure in the solution annealed condition and γ-fiber (<111>//ND) and β-fibre were seen in this condition. However, {110}<uvw> fibres mostly developed in the six-turn sample with texture components of E1 {011̅} < 111 >, E2 {01̅1} < 111 >, J1{01̅1} < 2̅11 >,J2 + {11̅0} < 1̅1̅2 >, D2 {1̅1̅2} < 111 > , D1 {112̅} < 111 > and F {110} < 001 >. In addition, the Cu{112}〈111〉 component was significantly diminished. This weakened Cu{112}〈111〉 will enhance the mechanical properties, particularly the formability and toughness, as previously reported by the current authors. It was found that applying severe plastic deformation (SPD) in the form of HPT reduces the effect of martensitic texture in the solution treated steel.

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Identifiers

ORCID for Terence G. Langdon: orcid.org/0000-0003-3541-9250

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